Hi there, thanks for asking. This could be migraine
. These headaches
are unilateral in many cases. For you it has involved the left side of your head. However, if this is the first time you are experiencing such a headache, it is necessary to go to a doctor and he should see what is exactly the kind of headache you have. He should also investigate all the possible causes which may cause the secondary headaches. I wish you a good health.